Artificial Insemination (AI) is a reproductive technique that consists of placing sperm inside the feminine reproductive tract to shorten the distance the sperm must travel until they reach the oocyte.
Artificial Insemination was used initially in situations of anatomic alterations of the masculine reproductive system or in cases of erectile dysfunction, in which the male was not able to ejaculate inside the woman's vagina. Artificial Insemination was also used after that in cases of masculine infertility, since the concentration of the sperm allows a greater number to reach the surroundings of the egg.
Ejaculation by nature injects a great quantity of sperm into the entrance of the uterus, called the cervix or neck of the uterus. The glands of the cervix produce mucus that, unlike the acid pH of the vagina, is an alkaline pH just like the ejaculatory liquid. The sperm penetrate through this cervical mucus and are stored in crypts that are formed by the cervical glands. Many sperm do not penetrate the mucus and are lost in the vaginal area.
The semen or male ejaculatory fluid possess substances (prostaglandins) that act on the cervix contracting the uterus and absorbing the accumulated sperm into the cervical mucus toward the upper uterus. The ejaculatory liquid never enters into the uterine cavity, but remains in the vagina; this is why it is common for women to feel some liquid trickling down after having sexual relations. With Artificial Insemination, the ejaculatory liquid is separated from the sperm and is eliminated because, if left in the uterus, it could cause strong contractions or may even cause infections or anafilactic reactions.
Apart from the uterine contractions caused by the prostaglandins of the seminal plasma, the sperm rise towards the Fallopian Tubes through peristaltic contractions induced by the hormones liberated from the follicules. Normally, there is only one dominant follicule that will produce a larger quantity of hormones making its corresponding tube contract more than the other, thus absorbing the major part of the sperm.
When the sperm reach the zone where the oocyte is found, they have been subjected to series of transformations known as spermatic capacitation during their journey from the cervix. We know that the sperm found in the semen are unable to fertilize an oocyte and can only do so after going through this capacitation process. Once they have reached the oocyte through the swimming motion of their tale, the sperm penetrate the cells that surround the oocyte (these cells are called Cumulus Ooforus) and thanks to specific receptors in the Zona Pellucida (transparent membrane that envelopes the oocyte) they join with it causing a modification in the head of the sperm (called Acrosomic Reaction) freeing substances that change the Zona Pellucida thereby allowing fertilization. However, it seems that for fertilization to take place, a sufficient number of sperm must adhere to the Zona Pellucida. If only a few arrive, fertilization will be difficult to accomplish. This explains why males with a small amount of motile sperm have great difficulty in achieving natural pregnancy since, as already mentioned, a certain amount of these few motile sperm will be lost in the vagina. As for the rest, not all of them will manage to reach the upper uterus, and some of those that do, will go toward the Fallopian Tube that has not released an oocyte. And finally, not all the sperm that do reach the oocyte will be able to penetrate the Cumulus Ooforus cells and adhere to the Zona Pellucida. If we begin with a small number of sperm, very few will actually reach the oocyte. In these cases, Artificial Insemination is a very helpful and simple technique, since this process allows us to place a great number of motile sperm in the upper uterus so that a sufficient number actually reach the oocyte. In a schematic explanation of the process, the sperm are concentrated and deposited much closer to the oocyte. This way, the millions of sperm left along the path in the natural process, are not lost. The sperm in fact do not simply concentrate by themselves. Two hours before performing an Artificial Insemination, a process of artificial capacitation is carried out. This imitates the natural capacitation process which basically, apart from concentrating the sperm, consists of eliminating the ejaculatory liquid and it being substituted by a specific culture that helps increase the motility of the sperm and improve their fertilizing capacity. A selection of the best sperm is carried out and these are the ones used in the Artificial Insemination.
Different types of Insemination exist depending on the source of the semen and the location in the feminine genital tract where the sperm are placed:
Depending on the source of the sperm:
- AI by a partner (AIH), when the sperm come from the partner.
- AI by donor (AID), when the sperm come from an anonymous donor.
Depending on the area where the sperm are placed:
- Paracervical AI, when placed in the cervical canal.
- Intrauterine AI, when placed in the interior of the uterus.
An Intrauterine Artificial Insemination is normally performed with sperm previously capacitated, as this produces the best results.